Crystal oscillator watch

ABSTRACT

AN ELECTRONIC WATCH INLUDES A POWER SOURCE, A TIME BASE, A DRIVE CIRCUIT AND TIME INDICATING MEANS. THE TIME BASE IS A PIEZOELECTRIC CRYSTAL OSCILLATOR, SPECIFICALLY AN ASTABLE MULTIVIBRATOR HAVING A LOW DUTY CYCLE WHICH   PULSES THE CRYSTAL AT THE FUNDAMENTAL OR A SUBHARMONIC OF ITS NATURAL FREQUENCY.

March 2, 1971 B. SHRADY I 3,566,601

' CRYSTAL OSCILLATOR WATCH Filed Jan. 50, 1969 /40 M40 4/ l 4Z4 #2 2/ m 5 .32 v w I 14 j' 3; .294

INVENTOR. Aims a. Sl/EAD) United States Patent 3,566,601 CRYSTAL OSCILLATOR WATCH Lewis B. Shrady, Irvington, N.Y., assignor to Timex Corporation Filed Jan. 30, 1969, Ser. No. 795,242 Int. Cl. G04c 3/00 US. Cl. 5823 2 Claims ABSTRACT OF THE DISCLOSURE An electronic watch includes a power source, a time base, a drive circuit and time indicating means. The time base is a piezoelectric crystal oscillator, specifically an astable multivibrator having a low duty cycle which pulses the crystal at the fundamental or a subharmonic of its natural frequency.

The present invention relates to horology and more particularly to a watch utilizing an electronic crystal oscillator.

The accuracy of piezolectric crystal oscillators in timekeeping has been known. Generally, the high frequency of the crystal oscillator, the time base, for example, 10,000 Hz., is reduced by a count-down dividing circuit to a much lower frequency, for example, 3 Hz., to either directly drive time indicating hands or to synchronize a motor driving those hands. However, it has not been feasible to produce awatch using a crystal oscillator, primarily because of the problems of limited power and limited space.

A watch, particularly a wrist watch, is limited in its physical size. Too large or heavy a wrist watch, regardless of the accuracy of its timekeeping, is not acceptable. The limited size of the watch means that it can only contain a relatively small battery. i.e., a button cell. The watch should run at least one year without changing the battery cell, so that there is only a small amount of power available to operate the watch.

The size of the watch also presents a problem as to the piezoelectric crystal. In general, the lower the frequency of the crystal, the larger is its size. It is difficult to fit a crystal having a frequency of 500 Hz. into a watch case, as it is too large. The obvious solution is to increase the frequency and use a smaller crystal. However, the use of a smaller higher frequency crystal implies: (1) a requirement for more power, as the pulse rate to impulse the crystal rises to match the frequency of the crystal; and (2) a more complex count-down circuit, which is required to reduce the high frequency of the crystal oscillator to the much lower freqeuncy needed to operate the watch, the complex count-down circuit itself using relatively more power.

It is the objective of the present invention to provide a watch utilizing a crystal oscillator in which: (1) the oscillator is relatively small in physical size so that it may fit in a watch case; (2) the oscillator uses relatively little power so that the watch may be powered with a small battery cell; and (3) the output of the oscillator is of such a low frequency as to permit a relatively simple count-down circuit.

In accordance with the present invention, a watch is provided utilizing a crystal oscillator as its time base. The crystal oscillator is selected to fit within the watch case and preferably is no larger than one of the other components, for example, the battery cell. For example, the crystal may be a piezoelectric quartz crystal having a resonant (natural) frequency of 60,000 Hz. which can be /2-inch in length. The crystal is connected at one of the low impedance points of a regenerative freedback astable multivibrator. The astable multivihrator is preferably a 3,566,601 Patented Mar. 2, 1971 relaxation oscillator having a very short duty cycle and utilizing a complementary pair of transistors. The crystal is pulsed at a selected subharmonic rate of its resonant frequency, for example, of its natural frequency. This provides an output frequency of the multivibrator above a minimum threshold level, which is at the selected subharmonic of the resonant frequency of the crystal. The astable multivibrator is adjustable, for example, by changing the time constant of its resistor-capacitor network, so that the crystal may be compensated for manufacturing tolerances and aging. Such compensation may occur at the initial manufacture of the watch or in its subsequent testing or repair.

Other objectives of the present invention will be apparent from the detailed description of the best mode of placing the invention into operation, which is described below in conjunction with the figures of the accompanying drawing. In the drawing:

FIG. 1 is a top plan partially cut-away view of the watch of the present invention; and

FIG. 2 is a schematic diagram of the preferred crystal oscillator.

In FIG. 1 the horological device of the present invention is shown as a wrist watch or other timepiece. The wrist watch includes a case 1 having a bezel 2. The crystal 3 covers a dial 4 having numbers 5 or other indicia of time. The time is indicated, as in conventional watches, by a seconds hand 6, a minutes hand 7, and an hours hand 8, which rotate from a common center 9. The power to operate the watch is derived from the small battery cell which is internal to the watch case 1. Alternatively, a solar cell or other electrical power source may be used. The battery cell 10 is connected to a time base 11 by means of line 12. The time base is a high-frequency piezoelectric oscillator. The high output frequency of the time base, by means of line 13, is provided to the dividing circuit 14, which counts down the high frequency of the time base. The output of the dividing circuit 14, by line 15, is connected to a drive circuit 16. The output of the drive circuit, by line 17, is connected to a coil 19 of fine wire. The battery 10 is used, as shown by line 26, to power the dividing circuit and, by line 27, to power the drive circuit.

The coil, when pulsed by the drive circuit, attracts the magnetic piece 20 fastened to the pivotable arm 21, which arm is returned to its normal position by the spring 22. A pawl 23, fastened on the upper end of the arm 21, indexes a rotatable index wheel 24. The index wheel 24, by means of a pinion (not shown), rotates a gear which, in turn, is connected to the other gears of the gear train of the watch. The train of the watch rotates the previously mentioned hands 6, 7 and 8.

Other types of transducers may be utilized to convert the electrical energy of the drive circuit 16 into the mechanical motion necessary to rotate the hands of the watch. Alternatively, the drive circuit 16 may operate electroluminescent or other types of electro-optical time indicating means. The term time display, as used herein, includes rotatable hands as shown in FIG. 1, electro-optical display means such as a series of bulbs arranged on the dial of the watch, and other types of time indicating mechanisms.

The circuit of FIG. 2 is a regenerative feedback astable multivibrator. Specifically, it is a relaxation oscillator utilizing a complementary pair of transistors. Preferably the circuit is formed by integrated circuit techniques. The cir cuit includes a first transistor which is the output transistor of the circuit and is an NPN transistor. The second transistor 31 of the circuit is a PNP transistor. These transistor types may be interchanged by changing the polarity of the power source. The collector of transistor 30 is connected to the positive terminal of the power source 10,

through resistor 36, the power source being, for example, the same small button type of battery cell 10 which is within the watch case. The base of transistor 30- is connected, through resistor 32, to the collector of transistor 31. The emitter of transistor 31 is connected, through resistor 33, to the collector of transistor 30. A resistor 36, representing the load, is positioned between the positive terminal of source 10 and junction 37. The junction 37 is connected to one side of a capacitor 39', the other end of which is connected to the base of the transistor 31. The,

base of the transistor 31 is also connected through the resistor 34 to the negative terminal of source 10. A piezoelectric crystal 40, for example, a quartz crystal, is connected in parallel with the resistor 33 and between the terminals 41 and 42. The crystal 40, of quartz or other piezoelectric material, exhibits a low impedance at its resonant frequency and a higher impedance at other frequencies. A capacitor 43, connected to junction 41, is connected through the resistance 44 to the negative terminal of source 10. A capacitor 39a is connected in parallel with resistance 32 between the collector of transistor 31 and the base of the transistor 30. A resistor 38 is connected to the base of transistor 30 and has its other terminal connected to the negative terminal of source 10.

The following values of the components of the oscillators are given by way of example only, as other values may be used, depending, for example, upon the frequency and voltage selected. The quartz crystal has a resonant frequency of 60 kilo Hz., asuitable cut being NT.

Resistor 36 (R1) of 47K ohms,

Resistor 33 (R2) of 47K ohms.

Resistor 32 (R3) of tolOK ohms. Resistor 34(R4) of 1.5 megohms. Resistor 44(R5) of K ohms. Capacitor 39(C1) of 100 picofarad. Capacitor 43(C2)of 600 picofarad. Capacitor 39(C3) of 0 to 100 picofarad.

In operation, when power is applied, transistor 31 conducts from base current applied through resistor 34. Transistor 31 supplies base current to transistor 30, which also conducts. As the collector of transistor goes to ground, capacitor 39 attempts to drive the base of transistor 31 more negative, thus increasing regenerative action. As capacitor 39 attempts to drive the base of transistor 31 goes slightly more positive, causing a regenerative action which cuts transistor 30 and transistor 31 off. The base ofi transistor 31 now goes toward ground at a rate determined by resistor 34, capacitor 39 and resistor 36. When the base of transistor 31 reaches the conductive state once more, the cycle repeats.

The short spikes at the collector of transistor 30 cause crystal 40 to emit a decaying train of oscillations. These appear across resistor 33 and cause the circuit to synchronize at the fundamental or a submultiple of the crystal frequency. A wide range of subharmonics can be utilized by proper choice of resistor 34 and capacitor 39. In addition, due to the very low duty cycle with transistors 30 and 31 on or off simultaneously, the circuit operates at very low power. The output frequency may be adjusted over a narrow range by choice of capacitor 43 and resistor 44, either one, or both, of which may be made adjustable. Crystal 40 operates into a fairly low impedance, thus improving stability with voltage and temperature. The crystal may be used in any low impedance portion of the circuit, such as across the resistor 36 if desired.

I claim:

1. A timepiece comprising a power source; a high frequency crystal oscillator connected to said power source a count-down circuit connected to said power source and dividing the frequency output of said oscillator; a drive circuit connected to said power source and to said countdown; and time indicating means coupled to and driven by said drive circuit; wherein the crystal oscillator comprises an astable relaxation oscillator and a crystal which is impulsed by the astable relaxation oscillator at the fundamental of a subharmonic of its resonant frequency and wherein said astable oscillator includes a pair of complementary transistors as active elements thereof and a resistor and said crystal is connected in parallel and across said resistor to provide a low impedance input to said crystal.

2. A timepiece as in claim 1 wherein the oscillator includes an R-C network which is adjustable so that the said frequency may be changed.

References Cited UNITED STATES PATENTS 3,217,269 11/1965 Rowley et al 331-116 3,492,806 2/1970 Walton 5823 RICHARD B. WILKINSON, Primary Examiner E. C. SIMMONS, Assistant Examiner U.S. Cl. X.R. 3311l6 

